The use of molecular and cytogenetic methods as a valuable tool in the detection of chromosomal abnormalities in horses: a case of sex chromosome chimerism in a spanish purebred colt

Abstract

Chromosomal abnormalities associated to sex chromo-somes are reported as a problem more common than be-lieved to be in horses. Most of them remain undiagnosed due to the complexity of the horse karyotype and the lack of interest of breeders and veterinarians in this type of diagno-sis. Approximately 10 years ago, the Spanish Purebred Breed-ers Association implemented a DNA paternity test to evalu-ate the pedigree of every newborn foal. All candidates who showed abnormal or uncertain results are routinely submit-ted to cytogenetical analysis to evaluate the presence of chromosomal abnormalities. We studied the case of a foal showing 3 and even 4 different alleles in several loci in the short tandem repeat (STR) -based DNA parentage test. To confirm these results, a filiation test was repeated using fol-licular hair DNA showing normal results. A complete set of conventional and molecular cytogenetic analysis was per-formed to determine their chromosomal complements. C-banding and FISH had shown that the foal presents a sex chimerism 64,XX/64,XY with a cellular percentage of approximately 70/30, diagnosed in blood samples. The use of a di-agnostic approach combining routine parentage QF-PCR-based STR screening tested with classical or molecular cyto-genetic analysis could be a powerful tool that allows early detection of foals that will have a poor or even no reproductive performance due to chromosomal abnormalities, saving time, efforts and breeders' resources.